1. Field of the Invention
The present invention relates to devices and methods for controlling internal combustion engines and particularly to controlling internal combustion engines having a plurality of variable valve timing (VVT) mechanisms changing a phase in which at least one of intake and exhaust valves is opened/closed.
2. Description of the Background Art
VVT (Variable Valve Timing) has conventionally been known that changes a phase (crank angle) in which an intake valve or an exhaust valve is opened/closed, according to an operating condition. Generally, the VVT changes the phase by rotating a camshaft that causes the intake valve or exhaust valve to open/close. For example for a V-type engine a camshaft is provided for each bank or group of cylinders. Such an engine can be designed to cause only the camshaft associated with one cylinder group (or bank) alone to drive a fuel pump (a high pressure pump supplying fuel to an injector for injecting the fuel directly into a cylinder, in particular), a vacuum pump and other auxiliaries. In that case, the camshaft associated with one cylinder group is different from that associated with another cylinder group in rotational resistance and hence responsiveness to variation of the phase. As such, similarly (or concurrently) operating the VVTs associated with the camshafts, respectively, may not necessarily similarly (or concurrently) vary phases in which the intake and exhaust valves are opened/closed. In that case, one cylinder group receives an amount of air, while the other cylinder group receives a different amount of air. This disadvantageously facilitates the engine to rotate variably (in speed while the crankshaft rotates once) and significantly vibrate. Accordingly the responsiveness to variation of the phase must be considered in operating the VVT.
Japanese Patent Laying-Open No. 2003-172160 discloses a variable valve timing control device for an internal combustion engine that allows a plurality of cylinder groups to match in responsiveness of valve timing control if their camshafts are unbalanced in load torque by a load of auxiliaries. As disclosed in Japanese Patent Laying-Open No. 2003-172160, the variable valve timing control device for an internal combustion engine includes: intake and exhaust camshafts provided for each of a plurality of groups of cylinders of an internal combustion engine; a valve timing adjustment unit advancing or retarding the phase of the rotation of at least one of the intake and exhaust camshafts of each cylinder group relative to that of the rotation of the crankshaft to time at least one of intake and exhaust valves of each cylinder group to operate earlier or later; a control unit exerting valve timing control to control the valve timing adjustment unit of each cylinder group in controllability to match each cylinder group's actual valve timing to its targeted valve timing; auxiliaries driven by a camshaft of a particular cylinder group; and a correction unit reflecting the particular cylinder group's delay in responsiveness of valve timing control that is attributed to a load of the auxiliaries in correcting in controllability the valve timing adjustment unit(s) of the particular cylinder group and/or another cylinder group to match the particular cylinder group to another cylinder group in responsiveness of valve timing control.
As disclosed in the publication, the variable valve timing control device for an internal combustion engine allows a correction unit to allow a plurality of cylinder groups to match in responsiveness of valve timing control if the camshafts of the plurality of cylinder groups, respectively, are unbalanced in load torque by a load of auxiliaries.
However, if the valve timing adjustment unit is corrected in controllability to allow a cylinder group for which valve timing control responds with a delay and another cylinder group to match in responsiveness of valve timing control, as described in Japanese Patent Laying-Open No. 2003-172160, the plurality of cylinder groups nevertheless can have their valves differently timed to differently open/close. For example, if a camshaft is rotated by an electrically operated actuator (e.g., a motor or the like), the actuator requires a large current, since rotating the camshaft requires a large torque. In that case, concurrently operating electrically operated actuators associated with the cylinder groups, respectively, can result in an excessively increased load on an electric circuit energizing the actuators. This can result in the actuators receiving an insufficient current. As such, a cylinder group providing a response delayed by a load torque of the camshaft cannot be improved to be sufficiently fast in responsiveness and consequently cannot achieve responsiveness as requested. As a result the plurality of cylinder groups can have their valves differently timed to differently open/close.